Re: synchronized_standby_slots behavior inconsistent with quorum-based synchronous replication

On Thu, Mar 19, 2026 at 12:08 PM Hou, Zhijie/侯 志杰
<houzj(dot)fnst(at)fujitsu(dot)com> wrote:
>
> On Wednesday, March 18, 2026 6:38 PM Ashutosh Sharma <ashu(dot)coek88(at)gmail(dot)com> wrote:
> > PFA patch that addresses above comments.
>
> Thanks for the patch! Overall, I think this is a valuable feature as I've heard
> requests from many customers for a way to avoid blocking logical replication
> when only some instances are down when using synchronized_standby_slots.
>
> I didn't find any bugs in the patch, but I have a few comments on the code and
> tests:
>
> 1.
>
> > /*
> > * Return true if value starts with explicit FIRST syntax:
> > *
> > * FIRST N (...)
> > *
> > * This is used to distinguish explicit FIRST from simple list syntax whose
> > * first slot name may start with "first".
> > */
> > static bool
> > IsPrioritySyncStandbySlotsSyntax(const char *value)
>
> I think adding a new function to manually parse the list isn't the most elegant
> approach. Instead, it would be cleaner to have a new flag that distinguishes
> when a plain name list is specified, and use that to mark the case
> appropriately like:
>
> /* syncrep_method of SyncRepConfigData */
> #define SYNC_REP_PRIORITY 0
> #define SYNC_REP_QUORUM 1
> +#define SYNC_REP_IMPLICIT 2
>
> standby_config:
> - standby_list { $$ = create_syncrep_config("1", $1, SYNC_REP_PRIORITY); }
> + standby_list { $$ = create_syncrep_config("1", $1, SYNC_REP_IMPLICIT); }
>

I like the idea. The only thing we have to see is that the changes in
synchronous_standby_names for this look clean (converting IMPLICIT to
PRIORITY and overwriting num_sync to 1). Also, do you think
SYNC_REP_ALL is more meaningful than SYNC_REP_IMPLICIT?

thanks
Shveta